A third generation mobile telecommunications network 1 as presently proposed for the Universal Mobile Telecommunication System (UMTS) is shown in FIG. 1. It comprises a mobile terminal 2 that can be in communication with a public and coordinated mobile telephone network such as a UMTS radio access network (UTRAN) 4. The UTRAN 4 comprises a Radio Network Controller (RNC) 5 and one or more so-called “Node B” 3 each of which includes a base transceiver station. The UTRAN 4 is connected to a core network 6 which comprises two pathways: a voice message pathway via a Mobile Switching Center (MSC) 7 and Gateway MSC (GMSC) 9 providing a connection to other voice networks 10 such as a public telephone network or other mobile telephone networks (PLMN), as well as a data pathway via a Serving GPRS support node (SGSN) 11 and a Gateway GSN (GGSN) 13 to other data networks 14 such as the Internet. The core network 4 also comprises a Home Location Register (HLR) 15 for storing subscriber information and a reference to the location of mobile terminals 2 when used in combination with a Visiting Location Register (VLR) 8, each of which is associated with an MSC 7.
Third generation mobile telephone networks such as UMTS allow handovers between different systems, e.g. from UMTS to GSM and vice versa. Handover between systems can be necessary because, for instance, the GSM or UMTS network does not have the necessary geographical coverage—e.g. a mobile terminal moves out of the coverage area of one system into another, or because of congestion on one system, that is for load balancing, or to provide a different service, e.g. from UMTS to GPRS to provide specific data services.
To provide the necessary information for making the handover decision, the mobile terminal is able to make measurements of surrounding radio transmitters. Typical measurements are:                intra-frequency measurements on downlink physical channels at the same frequency or frequencies as the mobile terminal is using,        inter-frequency measurements on downlink physical channels at a frequency or frequencies that differ from the mobile terminal is using,        inter-system measurements on downlink physical channels belonging to a different radio access system,        traffic volume measurements on uplink traffic load,        quality measurements of quality parameters,        internal measurements of mobile terminal transmission power and received signal level,        measurements for implementation of Location Services, e.g. time of arrival information of various radio sources which may be used to provide a location for the mobile terminal.In addition the mobile terminal requires supplementary information such as cell information which allows the mobile terminal to monitor the various signals mentioned above. The mobile terminal sends measurement reports when certain criteria are met, e.g. periodically or event driven. The results of the measurement may be sent in a measurement report. Each measurement report is sent with a measurement identity number.        
Inter-system handover from UMTS to GSM and vice-versa for FDD outdoor systems are shown schematically in FIGS. 2 and 3, respectively. With reference to FIG. 2, a mobile terminal 2 is shown in communication with a UMTS radio access network (UTRAN) 4. The UTRAN 4 requests a measurement report either via a system information block (SIB type 11 or 12) on a broadcast channel or via a measurement control message on a dedicated channel. In these messages the UTRAN 4 provides the cell parameters of neighboring cells including those in other systems. These parameters are required to be able to perform measurements on candidate cells. The mobile terminal 2 provides the measurement report to UTRAN 4 on a dedicate channel. Based on the report a network element of the UTRAN 4 such as a Radio Network Controller (RNC) decides on the handover. The RNC sends a resource reservation request through to the target base station system (BSS) 16 of the GSM system via the relevant Mobile Switching Center (MSC) 17. BSS 16 sends a resource reservation acknowledgement and a GSM handover command to the RNC of the UTRAN 4. Subsequently, the RNC sends a handover from UTRAN command with the GSM handover command piggybacked on it. The mobile terminal 2 the changes to GSM and sends a handover access message to the base station transceiver of the target BSS 16. After handover is complete the BSS 16 initiates release of the radio resources in the UTRAN network, 4.
The reverse procedure is shown schematically in FIG. 3. Due to the similarity between UMTS and GSM, this procedure is similar to the one described with reference to FIG. 2. However, as the UTRAN handover command may be bigger than can be piggybacked in GSM, a pre-configuration mechanism is use, i.e. a reference number, each for a pre-defined set of UTRAN parameters.
The above described system handovers require close co-operation between the two systems. In particular, each system is subject to change, such as changing cell sizes, cell frequency allocations, number of cells. This information is communicated from on system to another via the Operation & Maintenance System (OMS). Two systems in which system information is exchanged between the relevant OMS will be called “coordinated systems”. This level of co-ordination however becomes increasingly difficult to implement as the number of alternative systems increases. The number of possible system handovers explodes rapidly, specially when multi-mode mobile terminals are used. A non-exhaustive list of systems follows which have different Radio Access Technologies (RAT's) and which might be relevant for a system change between any two: UMTS Frequency Division Duplex (FDD), UMTS Time Division Duplex (TDD), Multicarrier CDMA, GSM, GPRS/GSM, EGPRS/UTMS (GERAN), CDMA 2000, DECT, HIPERLAN/1 or /2, BLUETOOTH, OFDM (Orthogonal Frequency Division Multiplex) Local Area Networks. These radio access networks have different frequency ranges, different data rates, different modulation methods, etc. A testbed for such a multi-network has been described in “First step toward an IP-based VHE” by Morand et al., 3G Mobile Communication Technologies, 26–28 Mar. 2001, Conf Publication No. 477 IEE London. The networks considered were LAN, WLAN, UMTS and PSTN. Handover is managed by Mobile IP. Mobile IP is a protocol that provides address mobility on an IP network such as the Internet i.e. seamless transparent access to the Internet providing solution for the mobile nodes to move and attach anywhere on the Internet. However, it does not specify how a wireless message redirection or handover is to be carried out.
The present methods of dealing with change from one RAT to another require extensive knowledge to be available as to the protocols and parameters of the other candidate systems a mobile terminal might use.
The article “Blind radio access technology discovery and monitoring for software defined radio communication systems: problems and solutions”, Vardoulias et al., pages 306–310, 3G Mobile Communication Technologies, 26–28 Mar. 2001, Conf. Publication No. 477, IEE London describes some details of software defined reconfigurable mobile terminals capable of detecting and monitoring alternative RAT's which are net necessarily coordinated with a public mobile telephone system. However, a network organization in which these terminals may work is not discussed.
It is an object of the present invention to provide systems, apparatus and methods to allow a change of RAT even between uncoordinated radio access networks.